First-person shooter game

Open source first person shooter

Free fast paced arena shooter

A modern cross‑platform port of “STAR WARS™: Dark Forces” with mod support

Free agile arena shooter

Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy

Tank digging battle game

Source port for Build engine games

Yamagi Quake II is an alternative client for id Software's Quake II

Open Source voxel shooter

EDuke32 is an awesome, free homebrew game engine

A Quake mod based on the retro shooter SPRAWL

Fast paced, first person strategy game

The Free and Fast Arena Shooter

Game engine for Classic Doom

A free first person shooter for Mac, PC and Linux

Dhewm 3 is a Doom 3 GPL source port

Leading the way in newschool multiplayer Doom online

FPS aim trainer

The orb ponderer's arena first-person shooter

Epic story-driven FPS running on the Build Engine

Modern cross-platform port of the Descent engine

Shoot and survive

Top-down shooter action RPG

ReC98 source port of the first Seihou Project game

Game engine for Return to Castle Wolfenstein

A modernization effort of DOOM-3-BFG

First-person shooter with cooperative in-game map editing

Open source first person shooter

A Zandronum 3.0 fork with improved netcode, configurable movement and many small tweaks